Construction of silos

ABSTRACT

Silo includes interior radially extending hollow bodies each having an ogival cross-sectional shape. Inclination of walls of each body increases from its apex to its base. Interiors of bodies may be accessible from outside the silo. Hollow tubular element, terminating at its upper end in an ogival member, may be arranged along axis of silo and supported by the bodies. Each hollow body may carry an ogival roof capable of movement, e.g. vibration, with respect to the body. The sides of the bodies may be defined by distinct planes, each having a slope greater than the one above it. The tubular element may terminate at its bottom in telescopic elements which extend into a hopper.

United States Patent i lll 3,593,892

[72| Inventor Georges Leon Henri Petit l0 Auenue de Salonique, Paris, France [21| Appl. No. 801,402

[54] CONSTRUCTION 0F SILOS 17 Claims, 9 Drawing Figs.

1521 U.s.c| .l 222/200, 52/|97,222/156 {51} lm cl ..1204117/22,

065g 3/12, 365g 65/70 [501 Fieldofsearch 52/197.

2,563,470 8/1951 Kane 52/197 X 3,038,566 6/1962 Parsons 52/194 3,081,009 3/1963 Cooper 222/564 X 3,173,583 3/1965 Wahl 222/200 X 3,407,972 10/1968 Cymbalisty..4 222/196 X 3,435,993 4/1969 Hunkel 222/200 X Primary Examiner-Henry C. Sutherland Assistant Examiner-Sam D. Burke AnarneyBreitenfeld and Levine ABSTRACT: Silo includes interior [radially extending hollow bodies each having an ogival cross-sectional shape. Inclination of walls of each body increases from its apex to its base. interiors of bodies may be accessible from outside the silo. Hollow tubular element, terminating at its upper end in an ogival member, may be arranged along axis of silo and supported by the bodies. Each hollow body may carry an ogival roof capable of movement, eg. vibration, with respect to the body, The sides of the bodies may be defined by distinct planes, each having a slope greater than the one above it. The tubular element may terminate at its bottom in telescopic elements which extend into a hopper.

PATENIED JuLzo Isn SHEEY 2 0F 4 (rions: L. H. Pe'rrr PATENTED JuL20 aan SHEET l# F l1 INvEHTo'n.-

nTToRNE 4 5 CONSTRUCTION F SILOS The present invention relates to various improvements in silos, particularly as regards their shapes, structures and their internal geometry, with a view to facilitating the flow of products which are stored therein.

lt is known that a silo is essentially a container of cylindrical or prismatic form, terminated at its base by a hopper in the form of an inverted truncated cone or truncated pyramid. The flow of the contents of such a silo varies with large proportions, depending on the nature of the product, the filling conditions and the internal geometry of the silo. It is possible broadly to distinguish between three types of flow, namely, the mass flow, the chimney" flow and the funnel" flow. The diagrammatic FIGS. l, 2 and 3 of the accompanying drawings respectively illustrate these three types of flow.

In the mass flow (FIG. l), all the product P contained in the silo S becomes mobile as soon as the opening u of the hopper T is opened. There is an increase in the vertical velocity of the flow from the periphery of the silo S to its central axial zone. This speed gradient is more marked at the level of the hopper T; in FIG. l, the speeds of vertical descent of the contents of the silo are indicated by arrows which have lengths proportional to their speeds. Such a flow is the perfect flow, because it avoids any stagnation, which very often causes caking together, and permits complete emptying of the silo.

As the opposite of the mass flow, it is necessary to arrange for a chimney f'low. In this case (FIG. 2), only the zone disposed perpendicularly of the opening o of the hopper T is flowing, with creation of a central chimney. It is a question of a true vertical punching of the material under the shearing action of gravity. lf the gravitational effect is not sufficient to cause this shearing (along a vertical cylinder, the diameter of which is equal to that of the outlet), nothing moves in the silo, except for a meniscus situated just above the orifice, which is evacuated, leaving a stable initial arch in the form of a dome, the base of which is formed by the periphery of the outlet orilice. This method of flow is obviously the most unfavorable. lt is particularly met with loose granulated products or powders, especially when these products are very liable to clog or cake. It is pointed out that a generally hygroscopic product which shows a tendency to set as soon as it is made immobile for a fairly long time is qualified as being of the caking-type.

Finally, the flow usually takes place in funnel form (FIG. 3). ln this case, an initial chimney formation a is first of all formed at the upper part of the product P contained in the silo. As soon as this initial chimney has reached a certain height, the product which surrounds it flows by cleavage along a frustoconical surface C. The angle a of this frustoconical surface is different from the natural slope angle of the product. The emptying progresses in funnel formation because of successive cleavages along frustoconical cleavage surfaces such as C, Cl, C2, C3, C4. The emptying of the silo is onlytheoretically complete if the aperture angle of the hopper is smaller than the cleavage angle a. In the contrary case (FIG. 3a), a dead stock M which is never moved necessarily continues to exist at the bottom of the silo. This dead stock has obviously been represented in its minimum volume, corresponding to the differences in inclination between the cleavage surface C and the inclination of the hopper T, but in practice, the presence of such a dead stock produces clogging and the immobilized part of the silo can only become enlarged in time. Moreover, it frequently happens that the flow of a silo is disturbed because of the formation of stable accumulations and arches, which are due to high pressures occurring at the bottom of the silo. These may be domelike arches of the type of the initial arch as hereinbefore defined (appearing either at the commencement of emptying, or during the emptying, after considerable avalanches have occurred in the silo). It may also be a question of retaining rings of material in the form of circular arches accumulated at the periphery of the outlet orifice, with an inherent high cohesion (arching effect).

The presence, at the bottom of a silo of a considerable dead stock is a very widely occurring phenomenon; it is observed at the present time in all kinds of industries, the presence of dead stocks representing 20 to 60 percent of the volume of the silos. Numerous remedies for this retention of silos have been proposed. As it is generally out of tlhe question to act on the stored product so as to make it more flowable", for example, by bringing it into a condition in which it has low humidity and/or by reducing its compacting power, it is necessary to act on the silo. It is possible in this respect to use two main processes, namely, firstly the vibrating of certain parts of the silo, particuiarly the hopper, and secondly, a particular choice of the geometry of the silo, particularly as regards the shapes and distribution ofthe different structural elements encountered by the material contained in the silo and at the time of its descent.

lf numerous proposals have been made as regards the vibration of the silo, the geometry ofthe silo structure has not so far been given sufficient attention, taking into account its importance in the overall result.

Actually, if the reasons explaining the formation of dead stocks and arches at the lower part of the silo are analyzed it is necessary to consider as being essential the compacting and packing effects which are due to static pressures and espe cially to dynamic pressures. The static pressure at a point of the silo is the pressure at which the filling product is found to be subjected under the weight of the material which overhangs it; at a given point, it thus depends on the filling level of the silo. The dynamic pressure is that which results from the more or less great free dropping height ofthe product at the time when it is introduced into the silo: the sudden stoppage of the product against the wall of the hopper and then against the product already in position establishes a packing efect, showing a strong hysteresis.

In order to reduce the influence of the pressure factors referred to above, it has already been proposed to interpose horizontal floors known as decompression floors along the path of descent of the materials. The purpose of these elements is very simple: when the silo is being filled, they break the descending currents of product, thus reducing the compacting and the dynamic pressure. On the other hand, on emptying the silos, they reduce the static pressure for all the zone which they overhang. However, if such decompression floors are known in principle, it has appeared that they can still be greatly perfected, both as regards their shape, structure and their arrangement inside the silo, and these are the improvements which form one of the essential objects of the present invention.

According to a first feature of the present invention, as decompression elements, there are used hollow bodies, preferably prisms of ogival section having an inclination increasing from the apex to the base, these elements being disposed in a radial plane relatively to the axis of the silo, or more generally in a plane passing substantially through the axis of flow of each hopper.

According to another feature of the invention, these prisms forms cross members for the wall of the silo or of the hopper and the interior of said prisms is accessible from outside the silo.

According to another feature of the invention, each decompression prism comprises an ogival roof capable of slight loosening movements relatively to the prism assembly, which is fixed. The roof of each prism can be mounted on the prism by means of deformable systems, for example, rubber blocks. According to another feature of the invention, the roof of each prism can be associated with one or more vibrating elements.

According to another feature of the invention, the increasing inclination of the ogival elements of the decompression prisms is presented as a broken line comprising a succession of slope-interrupting points, these having the effect of restarting the flow.

According tok another feature of the invention, which can be combined with the aforesaid features, a hollow tubular elei preferably at its upper end, in an ogival member, the section of which has an increasing slope, which is preferably discontinuous.

According to another feature of the invention, the tubular chimneys are hereinbefore defined can end in one or more adjustable telescopic elements which can be brought to a relatively great depth in the bottom end of the silo and extend into the hopper.

Preferably, according to the invention, the tubular chimneys are held in position by means of hollow decompression prisms forming cross members, the interior of the prisms communicating with the interior of the chimneys.

According to another feature of the invention, in connection with silos having large dimensions, provision is made for operators to circulate inside the decompression prisms and the tubular chimneys. Observation and inspection windows are formed in the floor of the decompression prisms.

According to one particular embodiment of the invention for a silo as a body of revolution about a control axis, the silo is equipped with a tubular axial chimney held in position by at least one assembly comprising two radially disposed decompression prisms which are disposed crosswise in a horizontal lane. p Finally, according to another feature of the invention, the slope of the outlet hopper increases progressively from top to bottom by varying values.

It will be better understood how the invention can be carried into effect from the following description and the accompanying drawings, given as nonlimiting examples.

In the accompanying drawings, FIGS. l, 2, 3 and 3a have already been discussed.

FIG. 4 represents as a vertical axial section a silo which is a cylinder of revolution and comprises, according to the invention, a central tubular chimney which is held in position by decompression prisms.

FIG. 5 is a sectional view along the line V-V of FIG. 4.

FIG. 6 is a horizontal section along the section line VI-VI of FIG. 4.

FIG. 7 represents the section of a decompression prism, showing how a vibrating roof can be arranged above it.

FIG. 8 is a diagrammatic view as a vertical section of a silo comprising a plurality of outlet hoppers and equipped with decompression prisms according to the invention.

The improved silo according to the invention, as shown in FIGS. 4, 5 and 6, will now be described, it being understood that this is only given as a very simple example of how the invention can be carried into effect in a cylindrical silo.

Throughout the following description, the main concern is the structure of a silo in its upper part, comprising the shaft extended by at least a first hopper, these elements being assumed to be fixed, i.e. unvibrated. It must be understood that other hopper stages (capable of being vibrated) can be mounted so as to follow the first, in order to bring the products to an extractor. On the other hand, it is always supposed that the outlet of this first hopper is of suitable dimensions so as to approach as far as possible the section of natural fiow, this latter generally being prohibitive; in other words, one has to be certain that no serious error has been committed in the general outlet profile of the hopper and in the relative dimensions of the hopper and shaft (see on this subject, for example, the article by Andrew W. .lenike, entitled Design your bins for free flow" which appeared in Journal Modem Materials Handling," Nov. 1964)..lt would obviously be illogical to assume to improve the internal geometry of a silo without taking into account the already established optimum in respect of the general profile and the relative dimensions of the outlet hopper.

The silo comprises, in a manner known per se, and about a central axis AA, a substantially cylindrical main body 10 and a substantially frustoconical hopper ll. Situated beneath the hopper ll is an extractor assembly l2, which can be fed by a decompression hopper 13, which may be vibratable.

According to the features of the invention, a tubular central chimney I4 is mounted along the axis AA,l said chimney being terminated at its upper end by a preferably `Aremovable ogival member l5.

The assembly 14, l5 is held in position by two hollow prism stages disposed crosswise at two different levels, namely, the hollow prism assemblies 20 and 2l.for the upper level and 30 and 3l for the lower level.

The crosswise prisms 20, 2l thus serve as cross members for the entire silo structure. They are hollow and accessible from outside the silo. In respect of silos having large dimensions, the interior of said prisms is thus accessible to a workman. In this case, it may be advantageous for holes 20h, 2lb, 30h, 31h (see FIG. 6), to be formed in the floors 20a, 21a, 30a, 31a of the prisms, said openings pennitting the interior of the silo to be inspected. By means of these openings, which are preferably covered by grids which are themselves covered by dusttight doors, it is possible to observe the state of flow ofthe materials contained in the silo and to take the necessary countermeasures (for example, the vibration of the hopper 13) as soon as the commencement of a clogging action or an arch is confirmed or detected.

This new possibility will permit rapid progress to be made in this art, because of the observations and the measurements (various characteristics are regards flow, pressure, speed, etc. made on a large industrial scale and with silos of normal materials, whereas hitherto it was necessary to use the smallsize model made with transparent materials, and thus of different characteristics which adversely affected the value of the tests.

The use of hollow prisms in accordance with the invention also provides other very interesting possibilities: it is possible to control, supervise and maintain the internal state, Awhich could deteriorate, and it is possible to cleanse the internal atmosphere of the prisms, by regulating the air circulation therein; in particular, the interior of the prisms can be heated, this causing at little cost the heating of the zones of material in the vicinity of the prisms; this last possibility is very interesting, for avoiding the effects of a prolonged frost on materials with a high moisture content.

According to one important feature of the invention, the ogival member such as I5, the prisms such as 2l and the hopper such as ll, have a wall comprising a slope increasing progressively from top to bottom by discontinuous values; the sections of the three elements as above defined are thus shown as broken lines O, B, C, D; O', B', C', D; O", B", C", D". It appears experimentally that the increasing slopes assist the flow of the materials and that the discontinuous increasing inclinations themselves represent an optimal value: a discontinuous slope, because of the restarting effect, causes the materials to be held up much less than with a continuous slope. For example, the slope can increase in a uniformly discontinuous manner of x degrees for equal variations in level.

With the method of construction shown in FIGS. 4, 5 and 6, very many advantages are obtained; first of all the presence of a central tubular chimney terminated at its upper end by an ogival member I5 avoids the formation of a preferential central flow chimney when the material of the silo flows: the product is only able to flow by passing around the central tubular chimney; this means that all the material in the silo has a tendency to be moved when there is a flow. The zone with a stagnating tendency is forced to move. Furthermore, in the case where the silo is charged by pouring in the direction of the arrow F (FIG. 5), the presence of the ogivalmember I5 breaks up the pouring stream, thereby contributing to the reduction of the dynamic pressures created at the time of filling.

The decompression prisms 20, 2l, 30, 3l serve a similar purpose in respect of the dynamic pressures; furthermore, because of their level in the silo, they also contribute to reducing the static pressures.

Although the two cruciform decompression prism stages 20, 2l and 30, 3l in the embodiment shown in FIGS. d, 5 and 6 have been represented as being centered in the same axial planes passing through AA, they could with advantage be centered in axial planes which form between them an angle of 45, the prisms of one stage being thus centered along the planes X-X and the decompression prisms of the other stage along the planes Y-Y (FlG. 6).

In an interesting modification of the invention (FilG. ti), provision is made for the central tubular chimney to be extended downwardly until it is in the hopper lll and possibly in the vibrated hopper 13. ln order to illustrate this, such an extension is shown in FIG. 5 in the form of a telescopic tubular element 40, 4l 42, indicated in broken lines. Such an element can be adjustable in height, even while the silo is being used. It is possible in this way to adjust the flow during operation. Such an arrangement, which forms part of the invention, is very interesting, because it permits the adaptation of the length of the tubular central chimney to the nature of the product contained in the silo. More elaborate arrangements be used; for example:

a. it is possible to use a mounting on a resilient system which permits the self-destruction of any unsymmetrical accumulation (mounting on a flexure or other spring or shockabsorbing blocks, with adjustment of the travel by means of stops);

b. in order to increase this selfdestructing effect, the external walls of the tube or tubes or the internal wall of the final hopper can be lined with a lining having a very different coecient of friction, and in an unsymmetrical manner;

. the terminal element 42 can be associated with a vibrator in order to facilitate the flow of the products in the vicinity of the narrowest flow section and in order to complete the actions of (a) and (b).

In its most simple constructional form (FIG. 5), each decompression prism (and moreover also the terminal ogival member l5), for example the prism 3l, is limited at its apex by a V-section fold 50 with its edge downwards; for the decompression prisms, such a fold is for example provided by means of a metal angle iron. The material in the silo is able to accu mulate on such a fold so as quickly to establish an antiwear point at the apex of the element.

ln the more complex embodiment which is shown in FIG. 7, a decompression prism, bearing the genera! reference 5t), comprises a main body Fill over which is a roof 52; the mounting of the roof 52 on the prism 5l is effected by means of elastically deformable elements, for example, rubber blocks 53 as shown. Thus, the prism has a roof which is displaceable, according to the vertical and oblique pressures which are applied to it. Such a construction avoids the undesirable accumulations and deposits, to the same extent as the form with an increasing slope of the roof. In an even more complex arrange ment` a vibrator 54 is provided to cause the roof to vibrate. it has to be pointed out that these different solutions are only made possible because ofthe first feature prov' ed according to the invention, namely the use ofaccessible prisms.

As already indicated above, the silo shown in MGS. d, 5S and 6 is only given as an example for a particularly simple case. lt has to be understood that the decompression prisms and/or the tubular axial chimneys according to the invention can be used with all types ofsilos: a tubular chimney will be able to be used with advantage in any case where there would otherwise be the danger of a preferential flow chimney appearing; the decompression prisms will likewise be used systematically in order to reduce the static and dynamic pressures: for a cylindrical silo of small height, there will for example be used a single cruciform prism stage; for silos of greater height, at least two superimposed stages will be used.

FlG. 8 shows diagrammatically the cross section of a lengthened silo comprising three outlets S S2, S3. ln this case, according to the invention, several decompression prisms intersecting" perpendicularly of the outlets, such as 70, lit), 8l, d2, are used for channelling the flow of material towards Sl, S2, S3, while avoiding the excessive increase in the static and dynamic pressures. FIG. 8 is only given as a diagrammatic example of how the invention can` be carried into effect in respect of noncircular silos. More generally, it must be understood that the present invention is not limited to the embodiments which have been described, but covers all modications thereot` which conform to the spirit of the invention.

lclaim:

ll. A silo for materials in granulated or powder form, comprising a body terminating at its lower end in an outlet assembly including at least one hopper, the contents ofthe silo moving through said body toward said outlet along at least one vertical flow axis, and a decompression assembly within said body disposed above said outlet assembly, said decompression assembly comprising at least one hollow element having an upwardly directed ogival crosssectional shape, said element being arranged transversely of said body and passing through said flow axis` the interior of said body completely surrounding said element so that material may flow from above said element and around its sides to a region within said body directly beneath said element, the interior of said element being accessible from outside the sillo and the interior being of such dimensions that a mechanic may perform selective operations therein throughout the axial extent thereof.

2. A silo as claimed in claim l, characterized in that each hollow eiement has an external ogival section having slopes which increase from top to bottom by discontinuous values, thereby forming a hollow decompression prism.

3. A silo as claimed in claim l, in which the decompression assembly comprises at least one pair of hollow prismatic elements disposed crosswise in a horizontal plane.

d. A silo an claimed in claim 3 in which the two crosswise hollow prismatic elements are disposed at the base of said body where the latter joins said outlet assembly.

5. A silo as claimed in claim 1l, characterized in that each hollow element of the decompression assembly comprises a fixed lower part and an upper part which forms a roof and is capable of being set in vibration relatively to the fixed part.

6. A silo as claimed in claim i, characterized in that said decompression assembly comprises a tubular central chimney disposed in the axis of flow, said chimney being held in the silo body by means of hollow decompression elements extending perpendicularly of the axis of flow from the chimney to the wall of the shaft, these eiements being accessible from outside the silo.

7. A silo as claimed in claim o, characterized in that each hollow element has an ogivai external section with slopes or inclinations increasing from top to bottom by discontinuous values, thus forming a decompression prism.

8. A silo as claimed in claim 6, characterized in that the tu bular central chimney is connected to the wall of the shaft by at least two groups of hollow elements arranged crosswise in superimposed horizontal planes.

9. A silo as claimed in claim tl, characterized in that the crosswise groups of hollow elements are angularly offset in relation to the flow axis and the chimney.

lil. A silo as claimed in claim 6, characterized in that the tubular chimney comprises at its upper part an ogival member with an inclination increasing from top to bottom.

llll. A silo as claimed in claim ti, characterized in that the hollow elements have a prismatic section with an increasing slope from top to bottom.

i2. A silo as claimed in claim o, characterized in that the interiors of the elements communicate with the tubular central chimney interior.

i3, A silo as claimed in claim o, characterized in that each of the hollow elements comprises a fixed lower part and an upper part forming a roof capable of being vibrated.

telescopic assembly comprises a vibratable lower element.

l7. A silo as claimed in claim l; characterized in that the outlet assembly has downwardly converging walls, the slope of said walls progressively increasing from top to bottom by discontinuous values, the vertical profile of the hopper thus defining a broken line. 

1. A silo for materials in granulated or powder form, comprising a body terminating at its lower end in an outlet assembly including at least one hopper, the contents of the silo moving through said body toward said outlet along at least one vertical flow axis, and a decompression assembly within said body disposed above said outlet assembly, said decompression assembly comprising at least one hollow element having an upwardly directed ogival cross-sectional shape, said element being arranged transversely of said body and passing through said flow axis, the interior of said body completely surrounding said element so that material may flow from above said element and around its sides to a region within said body directly beneath said element, the intErior of said element being accessible from outside the silo and the interior being of such dimensions that a mechanic may perform selective operations therein throughout the axial extent thereof.
 2. A silo as claimed in claim 1, characterized in that each hollow element has an external ogival section having slopes which increase from top to bottom by discontinuous values, thereby forming a hollow decompression prism.
 3. A silo as claimed in claim 1, in which the decompression assembly comprises at least one pair of hollow prismatic elements disposed crosswise in a horizontal plane.
 4. A silo as claimed in claim 3 in which the two crosswise hollow prismatic elements are disposed at the base of said body where the latter joins said outlet assembly.
 5. A silo as claimed in claim 1, characterized in that each hollow element of the decompression assembly comprises a fixed lower part and an upper part which forms a roof and is capable of being set in vibration relatively to the fixed part.
 6. A silo as claimed in claim 1, characterized in that said decompression assembly comprises a tubular central chimney disposed in the axis of flow, said chimney being held in the silo body by means of hollow decompression elements extending perpendicularly of the axis of flow from the chimney to the wall of the shaft, these elements being accessible from outside the silo.
 7. A silo as claimed in claim 6, characterized in that each hollow element has an ogival external section with slopes or inclinations increasing from top to bottom by discontinuous values, thus forming a decompression prism.
 8. A silo as claimed in claim 6, characterized in that the tubular central chimney is connected to the wall of the shaft by at least two groups of hollow elements arranged crosswise in superimposed horizontal planes.
 9. A silo as claimed in claim 8, characterized in that the crosswise groups of hollow elements are angularly offset in relation to the flow axis and the chimney.
 10. A silo as claimed in claim 6, characterized in that the tubular chimney comprises at its upper part an ogival member with an inclination increasing from top to bottom.
 11. A silo as claimed in claim 6, characterized in that the hollow elements have a prismatic section with an increasing slope from top to bottom.
 12. A silo as claimed in claim 6, characterized in that the interiors of the elements communicate with the tubular central chimney interior.
 13. A silo as claimed in claim 6, characterized in that each of the hollow elements comprises a fixed lower part and an upper part forming a roof capable of being vibrated.
 14. A silo as claimed in claim 6, characterized in that the tubular chimney comprises at its lower end a telescopic assembly which is adjustable in height and which descends into the outlet assembly.
 15. A silo as claimed in claim 14, characterized in that at least part of the telescopic assembly is capable of being vibrated.
 16. A silo as claimed in claim 15, characterized in that the telescopic assembly comprises a vibratable lower element.
 17. A silo as claimed in claim 1, characterized in that the outlet assembly has downwardly converging walls, the slope of said walls progressively increasing from top to bottom by discontinuous values, the vertical profile of the hopper thus defining a broken line. 